CVE-2026-100770 in Firefox
Summary
by MITRE • 09/29/2026
Sandbox escape due to use-after-free in the DOM: Content Processes component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw represents a critical memory corruption issue within the Mozilla Gecko rendering engine, specifically affecting the Content Processes component responsible for handling Document Object Model operations. This vulnerability is classified as an use-after-free error, which occurs when software continues to utilize a pointer after the memory it references has been deallocated or freed by the system. In the context of web browsers, this typically happens during complex DOM manipulations where asynchronous events or rapid state changes lead to a race condition. An attacker can craft malicious HTML and JavaScript code that triggers specific sequences of element creation, modification, and removal. By carefully timing these operations, it is possible to force the browser to free memory associated with a DOM node while retaining a reference to that same memory location for subsequent processing steps.
When the application attempts to access or modify data through this stale pointer, it reads from or writes to an arbitrary region of memory rather than the intended object structure. This behavior aligns directly with Common Weakness Enumeration identifier CWE-416, which describes use-after-free vulnerabilities as a significant source of instability and security breaches. The operational impact is severe because modern browsers employ sandboxing techniques to isolate web content from the host operating system. However, an exploitation of this specific flaw allows malicious code running in a low-privilege browser tab or iframe to break out of its restricted execution environment. By manipulating memory layout through heap spraying techniques and leveraging the dangling pointer, an attacker can achieve arbitrary read-write primitives, which are essential for bypassing sandbox boundaries.
This escape mechanism falls under the MITRE ATT&CK framework category of Defense Evasion, specifically relating to process injection or container escaping depending on the specific exploitation chain employed. Once the sandbox is breached, the malicious payload gains execution capabilities with higher privileges than those granted to standard web content. This can lead to full system compromise, including data exfiltration, installation of persistent malware, and lateral movement within a network if the victim machine has broader access rights. The vulnerability highlights the inherent complexity in managing memory safety in high-performance rendering engines that must handle dynamic and unpredictable user interactions at scale.
To mitigate this risk, users are strongly advised to update their browsers immediately to Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, or Firefox ESR 140.17, as these versions contain the necessary patches that enforce stricter memory management protocols and prevent access to freed objects. Security administrators should ensure automated update policies are in place for all endpoints running affected browser versions. Additionally, deploying advanced endpoint detection and response solutions can help identify suspicious behavior patterns associated with sandbox escape attempts, such as unusual memory allocation spikes or unexpected process creation events originating from the browser binary. Continuous monitoring of vulnerability databases and prompt application of security patches remain the most effective defense against exploitation of these types of zero-day or recently disclosed flaws in widely used software components.